Confocal laser scanning microscopes perform better in resolution and contrast than conventional microscopes. In addition, unlike conventional microscopes, they provide resolution in the height direction of a sample. Therefore, confocal laser scanning microscopes are extensively used in, for example, the observation and measurement of biological samples and semiconductor samples. Confocal laser scanning fluorescent microscopes, which are a combination of a confocal laser scanning microscope and a fluorescent microscope, are used to observe the fluorescence of fluorescent substances in samples with the aid of a laser. Recently, confocal laser scanning fluorescent microscopes have been frequently used to illuminate a sample with multicolor (i.e., multi-wavelength) laser light and to observe multiple fluorescent substances that emit different wavelengths of fluorescence so that the multiple fluorescent substances may be separately detected.
In Japanese Laid-Open Patent Application No. H10-206742, a confocal scanning fluorescent microscope having independent scanning optical systems and lasers that emit laser light at different wavelengths (and are thus used for different purposes) are independently controlled so as to illuminate samples. With this technique, living cells can be observed while stimulating them with laser lights at different wavelengths. However, this technique has a problem in that aberrations occur when combining the light from lasers having different wavelengths, thereby deteriorating the imaging performance.